There is no federal regulation that prohibits a merchant from charging a fee for using a credit or debit card, although some states outlaw these surcharges.
According to Americans for Consumer Education and Competition (a group partially funded by Visa), states that prohibit all surcharges are: California, Colorado, Connecticut, Florida, Kansas, Maine, New York, Oklahoma, and Texas.
But even where a surcharge is legal, its generally a violation of Visa and MasterCards rules for a store to tack on a surcharge for their credit or debit cards. They define a surcharge as any fee that is charged for using the card that is not charged when another payment method is used. (Note: This rule does not apply when you pay your federal income tax with plastic.)
Heres a heads up for anyone with a Discover card merchants are allowed to pass along the cost of processing your transaction in the form of a surcharge. Discover dropped its no surcharge rule back in February, after negotiations with lawyers suing the major credit card companies. That federal antitrust suit was filed by a group of merchants who claim they are forced to raise prices because they cannot pass along the processing fees to cardholders. After agreeing to allow surcharges for its credit card and new debit card, Discover was dropped from that suit.